1. Field of the Disclosure
The present application relates to a liquid crystal display device, and more particularly to an array substrate of the liquid crystal display device and a fabricating method thereof which are adapted to provide light blocking films to the upper and lower sides of a thin film transistor, simplify the fabricating process, and reduce fabricating costs.
2. Description of the Related Art
In general, the driving principle of a liquid crystal display device is based on the optical anisotropic property and polarization property of a liquid crystal material. The liquid crystal molecules have a long and thin structure. As such, molecular arrangement of the liquid crystal material has a directional property. Also, the alignment direction of the liquid crystal molecules can be controlled by an electric field artificially applied to a liquid crystal material.
In accordance therewith, when the alignment direction of the liquid crystal molecules is arbitrarily controlled, the molecular arrangement of the liquid crystal material changes. The optical anisotropic property of the liquid crystal material enables light to be refracted along the controlled alignment direction of the liquid crystal molecules. As a result, an image can be displayed.
An active matrix liquid crystal display device (hereinafter, “AM-LCD device”) in which a plurality of thin film transistors and a plurality of pixel electrodes each connected to the respective thin film transistors are arranged in a matrix. The AM-LCD device has a high definition and a superior realization of a motion picture. As such, the AM-LCD device is being highlighted in a display industrial field.
The LCD device includes a color filter substrate (i.e., an upper substrate) on which a common electrode is formed, an array substrate (i.e., a lower substrate) on which pixel electrodes are formed, and a liquid crystal material interposed between the upper and lower substrates. Such an LCD device drives the liquid crystal material by applying a vertical electric field between the pixel electrode and the common electrode. As such, the LCD device has superior transmittance, a high aperture ratio and so on. A related art array substrate for an LCD device will now be described referring to FIG. 1.
FIG. 1 is a cross-sectional view showing an array substrate of a first related art LCD device. The array substrate of the first related art LCD device includes a gate line (not shown), a data line (not shown) and a thin film transistor which are formed on a transparent insulation substrate 10. The gate line and the data line cross each other with a gate insulation film 12 therebetween. A pixel region is defined by the gate and data lines crossing each other. The thin film transistor is formed at an intersection of the gate and data lines.
The thin film transistor includes a gate electrode 11 extended from the gate line, the gate insulation film 12 formed on the entire surface of the substrate 10 which includes the gate electrode 11, a semiconductor layer 13 formed on the gate insulation film 12 opposite to the gate electrode 11, and source and drain electrodes 15 and 16 formed in such a manner as to partially overlap with the semiconductor layer 13 and be separated from each other.
Also, the related art array substrate includes a passivation film 17 formed on the entire surface of the substrate 10 which is provided with the source and drain electrodes 15 and 16. The related art array substrate further includes a pixel electrode 14 which is formed on the gate insulation film 12 and electrically connected to the drain electrode 16 of the thin film transistor.
Although it is not shown in the drawing, the first LCD device includes the above-mentioned array substrate (i.e., a thin film transistor substrate) and a color filter substrate configured to face each other. The first LCD device further includes a liquid crystal layer interposed between the color filter substrate and the thin film transistor substrate.
The thin film transistor substrate is defined into a plurality of pixel regions. The thin film transistor, the pixel electrode 14 and a common electrode (not shown) are formed in each pixel region. The pixel electrode 14 and the common electrode are arranged alternately and parallel with each other on the same substrate and separated from each other.
The color filter substrate includes a black matrix which is formed on an opposite region to the gate and data lines formed on the thin film transistor substrate and the thin film transistors formed at the intersections of the gate and data lines. Also, the color filter substrate includes color filters formed opposite the respective pixel regions. In accordance therewith, the liquid crystal layer is driven by a horizontal electric field formed between the common electrode and the pixel electrode 14.
However, the related art LCD device forces the thin film transistor, which includes the source 15 and drain 16 electrodes and the semiconductor layer 13 forming a channel from the source electrode 15 to the drain electrode 16, to be perfectly exposed to external light including sunlight. As such, external light and light being scattered or reflected within the device can irradiate to the channel of the thin film transistor.
In other words, the related art LCD device cannot prevent external light and internally scattered or reflected light which are irradiated from the upside of the thin film transistor into the channel, thereby causing a leakage current in the channel. Due to this resulting leakage current, errors can occur in the image produced by the LCD device. More particularly, the channel portion of the semiconductor layer exposed to light cannot function as a channel because of the resulting leakage current. As such, it is difficult to control a variety of voltages which are necessary to drive the LCD device. Therefore, performance of the LCD device must deteriorate.
To address this matter, an LCD device including light blocking film patterns which are disposed at the up and down sides of the channel of the thin film transistor has been proposed.
FIG. 2 is a cross-sectional view showing an array substrate of a second related art LCD device. Referring to FIG. 2, the array substrate of the second related art LCD device includes: a first insulation film 30 formed on a transparent insulation substrate 20 and configured to have a opening; a first light blocking film pattern 31 formed on the first insulation film 30 provided with the opening; and a first gate insulation 32 formed on the entire surface of the transparent insulation substrate 20 provided with the first light blocking film pattern 31. Also, the array substrate includes: a gate electrode 21 formed on the first gate insulation film 32; a second gate insulation film 22 formed on the first gate insulation film 32 provided with the gate electrode 21; a semiconductor layer 23 formed on the second gate insulation film 22 and overlapped with the first light blocking film pattern 31; a pixel electrode 24 formed on the second gate insulation film 22 in such a manner as to be separated from the semiconductor layer 23; a source electrode 25 formed on the semiconductor layer 23; and a drain electrode 26 directly connected to the pixel electrode 24 and formed in such a manner as to be separated from the source electrode 25. The array substrate further includes: a passivation film 27 formed on the entire surface of the transparent insulation substrate 20 provided with the source and drain electrodes 25 and 26; a second light blocking film pattern 40 formed on the passivation film 27 and overlapped with the first light blocking film pattern 31; a second insulation film 28 formed to cover the passivation film 27 provided with the second light blocking film pattern 40; and a plurality of branched common electrodes 29 formed on the second insulation film 28 and overlapped with the pixel electrode 24.
In this manner, the first and second light blocking film patterns 31 and 40 disposed in the upper and lower sides of the thin film transistor shield light irradiated from a backlight unit onto a channel region of the thin film transistor. As such, the second related art LCD device can prevent the generation of a leakage current in the thin film transistor.
However, in order to form the array substrate of the second related art LCD device, a first masking procedure for forming the first insulation 30 with the opening, a second masking procedure for forming the first light blocking film pattern 31, a third masking procedure for forming the gate electrode 21, a fourth masking procedure for forming the semiconductor layer 23, a fifth masking procedure for the pixel electrode 24 separated from the semiconductor layer 23, a sixth masking procedure for forming the source and drain electrodes 25 and 26 on the semiconductor layer 23 and the pixel electrode 24, a seventh masking procedure for forming the second light blocking film pattern 41, and a eighth masking procedure for forming the common electrode 29 must be performed. Moreover, when a gate pad and a data pad, which are not shown in the drawing, are formed at ends of the gate and data lines, a ninth masking procedure for forming contact holes partially exposing the gate and data lines can be additionally performed.
In this way, a total of nine masking procedures are necessary to fabricate the array substrate of the second related art LCD device. A large number of masking procedures increases fabricating costs, the number of process steps and the probability of generating faults.